Limit `EarthRangerIO` `sub_page size` to a maximum value of 4000

[atmorling]

As this issue, and its fix demonstrates that the default sub_page_size value is actually the maximum supportable by the upstream API.
We should either:

• Allow the client to throw an exception on init if a value > 4000 is provided.
• Truncate values > 4000 to 4000 and provide a warning